The Czech club have an option to buy Mabil, who made just five league appearances for Cadiz after moving to Spain on a four-year deal in May 2022.
Mabil, who made just two appearances at the World Cup for a total of 22 minutes, is linking up with his former FC Midtjylland coach Brian Prisk at Sparta and hopes to return to his best form there.
"Under him I played my best football before," the 27-year-old told Sparta's website.
"I know he knows me very well and I know him very well.
"He's a very ambitious guy so we match the same ambitions.
"His way of looking at football is amazing and I got to experience that in Denmark. So I would really like to experience it again here."
Sparta currently sit third in the Czech First League, seven points off top spot, and Mabil was keen to elevate them into contention.
"I want to challenge for titles," he said.
"So for me the biggest motivation for coming here is to win and compete for the title and also to play in Europe again.
"I played in Champions League before with my old team in Denmark. It was a great feeling and I would love to have that feeling again.
"That's the goal for me here - to win titles and also be in the Champions League."
